1. Field of the Invention
The present invention relates to an optical disc camcorder, in particular, the invention relates to means for correcting a skew which is caused between an optical disc and an optical pickup unit by effect of rolling generated in the camcorder.
2. Description of the Related Art
Basically, an optical disc camcorder integrally comprising a camera unit and a recorder unit using an optical disc as its recording medium converts video and audio data received by the camera unit into AV data signals for recording them onto the optical disc and then records the converted digital signal onto an optical-disc track via an optical pickup system.
The optical pickup system executes recording of data signal by varying composition of the recording surface of the optical disc by way of condensing laser beams emitted from a semiconductor laser making up the light-emitting source onto an objective track position on the optical disc as of a minimal spot form via intermediate optical components and a laser-emitting object lens. Further, the optical pickup system executes reproduction of data signal by way of reading reflective light from the optical disc as an electrical signal via photoelectric conversion element such as a photo-detector or the like.
The object lens of the optical pickup system for emitting laser beam is subject to focus control performed against optical disc recording surface set to a biaxial actuator and also subject to tracking control in order that a condensed light spot can precisely follow up the track on the optical disc.
Perpendicularity between an optical axis of the object lens and the recording surface of the optical disc is one of extremely important factors to determine signal recording and reproduction characteristics. Deflection of the perpendicularity is called “skew”. For any reason, if the optical disc ever deforms, a skew is generated between the optical axis of the object lens and the recording surface of the optical disc. This in turn causes aberration including coma aberration, astigmatic aberration, spherical aberration, or the like, to be generated in the light spot condensed onto the optical disc, thus degrading signal recording and reproduction characteristics.
FIGS. 18A and 18B are explanatory views of “skew” phenomenon, in which FIG. 18A designates a case in which no skew is present, and FIG. 18B designates a case in which a skew is generated. FIG. 18A shows a case in which optical axis C of the object lens of an optical pickup system 2 correctly matches the normal line (the line perpendicular to the optical-disc surface) of an optical disc 1. FIG. 18B shows a case in which the optical disc 1 is tilted to cause the normal line P to be inclined against the optical axis C of the object lens of the optical pickup system 2, whereby resulting in the occurrence of the skew.
FIGS. 19A and 19B graphically designate variation of RF-jitter components (high-frequency jitter components) during the signal reproduction process in accordance with the variation of “skew”. The expression “Rad” direction indicates a seek direction of the optical pickup system 2, i.e., the normal line direction of the track of the optical disc 1. The expression “Tan” direction indicates a tangential direction of the track of the optical disc 1. As exemplified in FIGS. 19A and 19B, generation of even the slightest degree of skew in the “Rad” and “Tan” directions causes the jitter components to be grown very sharply.
Whenever being used for broadcast stations or AV-related business sectors, higher picture quality, higher audio quality, and higher reliability, are essentially demanded for the optical disc camcorders at large.
FIGS. 20A and 20B exemplify overall configuration of such a high-performance optical disc camcorder, in which FIG. 20A designates a rear view, whereas FIG. 20B designates a lateral view. Likewise, FIGS. 21A and 21B exemplify posture of image-pickup operation by way of actually using the optical-disc camcorder, in which FIG. 21A designates a rear view, whereas FIG. 21B designates a lateral view.
Actually, any of conventional optical-disc camcorders has realized such a dimension and weight substantially being equivalent to those of any camera-combined VTR making use of a conventionally available videotape as a recording medium. In terms of the image-pickup posture using such a conventional optical disc camcorder, as is shown in FIGS. 21A and 21B, while a photographer remains still, the camera (i.e., an optical-disc camcorder) is rarely affected by oscillation. However, when performing image-pickup operation while the photographer moves on himself (while keeps on running himself for example), the camera may hit against his head, and then, as is shown in FIGS. 22A and 22B, oscillation will act itself as rolling force in the direction R. When the photographer performs image-pickup operation at a low angle while bearing the camera with his hands, oscillation similar to the above case will affect the camera body. This is called “rolling phenomenon” of the camera body.
Once the rolling phenomenon is generated in the camera main body, the rolling effect is transmitted to the base plate assembly (a mechanical block being composed of an optical pickup system, a seek mechanism thereof, a spindle-motor chucking mechanism and an optical disc) inside of the main body, whereby causing gyro-moment to act on an optical disc 8 being rotated inside of the main body to cause the optical disc 8 to be deformed as shown in FIGS. 23A and 23B. Referring to FIG. 23A, X designates a horizontal axis against the camcorder main body 4 passing through the center of the rotation of the optical disc 8, where the horizontal axis X is in the direction identical to the optical axis of a camera lens 7 and also identical to the seek direction of the optical pickup system 2. On the other hand, Y designates a vertical axis against the camcorder main body 4 orthogonally intersecting the horizontal axis X via the center of the rotation of the optical disc 8. R designates a rolling direction, J designates a direction in which a gyro moment is generated, and D designates a direction in which the optical disc 8 rotating in the direction S is deformed by the gyro moment. FIG. 23B shows an upper surface portion of the camcorder main body 4 shown in FIG. 23A, in which Z designates an axis of the rotation of the optical disc 8. Because of the deformation of the optical disc 8, the above-referred skew is generated between the optical axis of the object lens of the optical pickup system and the optical-disc recording surface, whereby resulting in the degraded signal recording and reproduction characteristics.
As described above, any of the conventional optical-disc camcorders using an optical disc as the recording medium is subject to generation of rolling phenomenon to cause gyro-moment to affect the rotating optical disc to further cause the optical disc to be deformed, and yet, the rolling also causes spindle-motor shaft rotating itself in linkage with the optical disc to incur swing movement (or tilt). As a result of the deformation of the optical disc, skew (in other words, deflection in the perpendicularity) is generated between the optical axis of the object lens of the optical pickup system and the optical-disc recording surface, thus degrading signal recording and reproduction characteristics. And yet, swing movement of the spindle-motor shaft deflects track to result in the degraded tracking performance.
To cope with externally applied oscillation or shock incurring to any of the conventional optical-disc camcorders, such a shock-proof structure to prevent the base plate assembly from directly incurring oscillation and shock by way of protecting the base plate assembly inside of the main cubic-type casing with a spring or a rubber damper has been adopted.
Nevertheless, it has not been possible to fully shield oscillation and shock incurring to the base plate assembly merely by means of the conventional spring or rubber damper. Actually, once rolling phenomenon ever occurs in the main casing, rolling phenomenon still affects the base plate assembly to subsequently cause the optical disc to incur gyro moment, whereby generating skew between the optical axis of the object lens of the optical pickup system and the optical-disc recording surface, and yet, it also causes tilt (swing movement) to be generated on the part of the spindle motor shaft to cause signal recording and reproduction characteristic and the tracking performance to eventually incur degradation.
Actually, any of the above-cited conventional optical-disc camcorders is subject to electrical control in order that distance between the object lens of the optical pickup system and the optical-disc surface can be held constant (in other words, within focal distance of the object lens, more precisely, within focal depth range) as of the condition in which the optical pickup system executing signal recording and reproduction is not in contact with the optical disc. Nevertheless, for any reason, if the optical disc ever deforms, perpendicularity between the optical axis of the object lens and the optical-disc recording surface deflects to cause skew to be generated. The skew gravely affects the signal recording and reproduction characteristic. In particular, it is known that, in the case of the optical disc camcorder, since rolling is generated during the image-pickup operation as was described above, gyro moment adversely affects the rotating optical disc to cause the optical disc to be deformed.